Magnetic recording systems, such as hard disk drives (HDDs), are the primary form of data storage and retrieval far most computer-based systems. In high capacity storage systems, magneto-resistive read sensors, commonly referred to as “MR sensors” or “MR heads,” are commonly used in HDDs due to their ability to read data at higher track and linear densities than competing technologies.
MR sensors detect changing magnetic fields through a resistive change in their sensing layers (often referred to as their “MR elements”) as a function of the strength and direction of magnetic flux passing through the sensing layer. MR elements tend to vary greatly in their resistances and sensitivities due to manufacturing variations and tolerances. The resistance of a single MR element may also change due to temperature or other conditions in the disk drive during manufacturing and use.
Unfortunately, the performance of an MR head is closely linked to a bias voltage applied to it, which may typically need to be around 150 millivolts and controlled to within a few millivolts tolerance. Still further, it is often advantageous to center such a bias voltage differentially to the ground level, and minimize noise in the bias voltage to improve performance.